The present invention relates generally to synchronous rotating machines. More particularly, the present invention relates to power leads for high temperature superconducting field windings in the rotor of a synchronous machine.
Synchronous electrical machines having field coil windings include, but are not limited to, rotary generator, rotary motors, and linear motors. These machines generally comprise a stator and rotor that are electromagnetically coupled. The rotor may include a multi-pole rotor core and coil windings mounted on the rotor core. The rotor cores may include a magnetically-permeable solid material, such as an iron-core rotor.
Conventional copper windings are commonly used in the rotors of synchronous electrical machines. Electrical resistance of copper windings, however, is sufficient (although low by conventional measures) to contribute to substantial heating of the rotor and to diminish the power efficiency of the machine. Recently, superconducting coil windings have been developed for rotors, which have effectively no resistance and are highly advantageous rotor coil windings.
Typical superconducting rotor windings are made from saddle shaped coils that are assembled around cylindrical shells for structural support. These saddle shaped coils are complex winding structures that are cooled in direct contact with cryogens. The power leads are also cooled by cryogens through parallel flow circuit paths that present a challenge to control flow rate and temperature stability in the high centrifugal acceleration fields.
In an exemplary embodiment of the invention, a power lead is provided for a high temperature superconducting (HTS) rotor winding coil. The power lead includes a heat station block attachable to a return flow tubing bulkhead, a ceramic insulator securable between the heat station block and the return flow tubing bulkhead, and thermally optimized current leads coupled with the heat station block. Preferably, the heat station block includes two half-blocks that are sized to sandwich the return flow tubing bulkhead, wherein the power lead includes two thermally optimized current leads, one each coupled with each of the heat station half-blocks. The half-blocks may be secured to each other with electrically insulated bolts. The ceramic insulator may be formed of one of beryllia and sapphire and may be metal plated on both sides excluding edges thereof. The thermally optimized current leads are particularly configured with a cross-section, length and electrical resistance to carry rotor current with margin for transients while minimizing heat transfer as a result of ohmic resistance heating and thermal conduction heat transfer.
In another exemplary embodiment of the invention, a power lead for an HTS rotor winding coil includes heat station blocks electrically couplable with a rotor of an electrical machine. The heat station blocks are electrically insulated from a return flow tubing while being thermally coupled with the return flow tubing via a ceramic insulator interposed therebetween for thermal conductivity between the heat station blocks and the return flow tubing.
In yet another exemplary embodiment of the invention, an electric machine includes a stator and a rotor coupled with the stator for rotation relative to the stator about a rotor axis. The rotor includes lead terminals disposed in a vicinity of the rotor axis. A return flow tubing is provided for carrying a coolant for heat exchanger cooling, and an HTS rotor winding coil is coupled with the rotor lead terminals via the HTS power leads of the present invention. Lead sections of braided copper or the like are preferably coupled between the heat station block and the rotor lead terminals.